1. Technical Field
The present invention relates in general to a calibration apparatus for information storage systems, and in particular to a calibration apparatus for an information storage system that writes in multiple modes.
2. Description of the Related Art
Optical disk drives must be calibrated in order to maximize the signal-to-noise ratio (SNR) of the optical disk drive, among other specifications. Typically, the calibration system will set the laser write power and methodology to an optimum level for a given read head and optical disk media to maximize the SNR. Since this optimal level or operating point may vary with different optical drives and disk media, the write conditions of the optical disk must be optimized for each drive/media combination.
Because many drives can write data in multiple modes (a multi-mode drive) and because different types of information media can be loaded into the disk drive, the calibration cannot be fixed on the manufacturing line since the final drive/media combination is unknown. For example, a multi-mode drive may write to an optical disk using either Pulse Position Modulation (PPM) or Pulse Width Modulation (PWM) records, and either one of these writing modes may be used with any type of optical disk media, including rewritable media types such as Phase Change (PC) or, Magneto-Optical (MO), and Write Once Read Many (WORM). Therefore, in order to set the optical disk drive to the optimal write operating level and methodology, a calibration device is built into each optical disk drive that performs measurements on the disk drive readback signal to determine the performance of the disk drive once the configuration has been set. These measurements are then processed by the controlling microprocessor to adjust the write power and methodology, to achieve optimum performance of the optical disk drive. This calibration can be performed by the hardware every time a new disk is inserted in the drive or a new write mode is selected. Alternately, calibration can be performed as part of write Error Recovery Procedures (ERPs). Because there are multiple drive/media combinations and multiple write modes, different calibration parameters typically must be measured for each mode of operation and combination of the optical disk drive.
In order to support calibration in any of the various modes of operation, an optical disk drive may require a number of calibration devices that each measure a different parameter of the readback data. Each calibration device goes through a cycle of reading a test pattern or data that is first written to the disk and then measuring the average value of a particular parameter. If a given calibration mode requires measurement of multiple parameters, a number of these calibration cycles are required to complete the calibration measurements.
As will be appreciated, including many calibration devices in a single disk drive to support each of the multiple calibrations adds a significant amount of circuitry, consumes large amounts of power, and increases the cost of the optical disk or other type of drive. Moreover, a calibration requiring the measurement of multiple parameters typically will require multiple calibration cycles. What is needed is a calibration apparatus for an multi-mode drive that doesn't have substantially increased calibration hardware, but that can perform the various measurements required for all calibration modes of a multi-mode drive. Further, it would be desirable for such a calibration device to perform all calibration measurements for at least some calibration modes in a single calibration cycle. Such an apparatus would substantially reduce the cost and increase the speed of calibration for a multi-mode drive.